Trailers used to haul loose materials such as dirt, sand, gravel, or grain commonly have beds or tubs that have an open top with generally vertical front and rear walls and sloping sidewalls for retaining contents within the trailer. Therefore, if the trailer bed is not covered as the trailer is pulled over the road, the loose contents may be blown and scattered out of the open top of the trailer bed. Additionally, the contents of the trailer bed may be compromised by rain, or other contaminants. Accordingly, it is known to deploy tarps across the open top space of the trailer beds to cover the contents of the trailer beds.
Several mechanisms have been devised for deploying the tarps across the trailer bed. Many of these devices include radial arms that are rotatably mounted at the front and rear of the trailer bed and have a roll of tarp disposed between them. As the radial arms rotate in one direction across the truck bed, the roll of tarp between the arms is unrolled to cover the contents of the truck bed. When the arms are rotated back in the opposite direction, the tarp is taken back up upon the roll to uncover the trailer bed. Examples of such devices may be seen in Searfoss, U.S. Pat. No. 6,206,449 and in Michel, U.S. Pat. No. 5,002,328.
It is also common for these trailers to be adapted to dump their contents to one side or the other of the trailer, by elevating the opposite side of the trailer. In many of these side dump trailers, the trailers include a lip that projects outwardly along the side edges of the top periphery of the bed. As shown in the previously mentioned '449 patent, it is known and desirable to tuck the tarp roll underneath the projecting lip in order to store the tarp, especially during dumping operations, but also preferably when the tarp is fully deployed covering the trailer.
In order to tuck the tarp roll against the side of the trailer, it is known to attach the tarp roll to extensions that are pivotally connected to the free ends of the radial arms. According to one design, the radial arms are biased towards the covered side, and a motor attached to one of the extensions rotates the tarp roll to pull the tarp back across the trailer bed to the open configuration. Springs may be used to bias the extensions relative to the radial arms. According to one design the springs used to bias the extension relative to the radial arm are spiral torsion springs similar to those shown in Searfoss, U.S. Pat. No. 5,944,374.
The trailers of the type discussed above occasionally need to be provided into locations where the rear of the trailer is close against an obstruction, such as a building, tree, or overhang. In these instances, it is desirable to have the top of the radial arms be close to the trailer bed to minimize any interference by the tarp deploying apparatus with obstructions behind the trailer.
The tarp deploying mechanisms of the type discussed above occasionally have difficulty moving out of the stored and deployed position when they are tucked beneath the side lip. Furthermore, it can be difficult to obtain the correct biasing force for the radial arms, particularly as the apparatus ages and the resiliency or biasing force of the spring naturally diminishes.
Therefore, it is an object of the present invention to provide an improved tarp deploying apparatus generally of the type disclosed above wherein the ends of the arms used to deploy the tarp roll are brought in close proximity to a rear edge of the top of the trailer bed, wherein the apparatus is less prone to being stuck or hung up in the deployed and uncovered storage positions, and wherein the biasing force applied to the radial arms can be varied over time.